1. Field of the Invention
The present invention relates to a sheet processing apparatus and an image forming apparatus. More specifically, the present invention is suitably applied to a sheet processing apparatus that includes a plurality of sheet processing portions, and to an image forming apparatus, e.g., a copier or a laser beam printer (LBP), to which the sheet processing apparatus is connected.
2. Description of the Related Art
There has been conventionally proposed a sheet processing apparatus (hereinafter, “finisher”) included in a copier or the other image forming apparatus, and performing processes including such as a process for forming an image on a sheet such as a printed sheet by the image forming apparatus and a process for stitching sheets.
As such a finisher, there is known a finisher configured by a combination of first processing portion (hereinafter, “processing tray”) that registers and bundles a predetermined number of sheets and that wire-stitches a bundle of sheets (hereinafter, “sheet bundle”) if it is necessary to do so, and stacking means (hereinafter, “stack tray”) that receives and stores every registered sheet bundle or wire-stitched sheet bundle. Many techniques therefor including one disclosed in, for example, Japanese Patent Application Laid-Open No. 2-144370 have been already proposed.
The finisher often includes not only a conventional end stitching function of stitching the sheet bundle on its end but also a saddle stitching function of stitching the sheet bundle generally at its center, which function enables simple binding. Many techniques for the finisher of this type including one disclosed in, for example, Japanese Patent Application Laid-Open No. 11-322170 have been already proposed.
Further, as for the finisher that stacks a plurality of sheets conveyed from the image forming apparatus while a stitching process is being performed on the sheet bundle on the processing tray, and that discharges and registers the sheets to the processing tray after the stitching process, many techniques including one disclosed in, for example, Japanese Patent Application Laid-Open No. 10-194582 have been proposed.
The finisher includes, around the processing tray, a conveying path for conveying a sheet to the processing tray, a standby path (hereinafter, “buffer path”) for temporarily holding the sheet on standby, a buffer roller that conveys the sheet on the buffer path, a pair of sheet discharge rollers that discharge the sheet to the processing tray, a jogger that registers the sheets in a direction orthogonal to a sheet discharge direction while being moved in a front direction and a depth direction, a stapler that wire-stitches the sheet bundle, a pair of sheet bundle discharge rollers for conveying the sheet bundle on the processing tray to the stack tray, and the like.
Normally, the sheets discharged from an image forming apparatus main body are passed through the conveying path provided in the finisher, discharged to the processing tray by the sheet discharge roller pair, and sequentially stacked on the processing tray. The sheets discharged to and stacked on the processing tray are registered in the discharge direction whenever every sheet is discharged and then registered by the jogger in the direction orthogonal to the discharge direction. If a predetermined number of sheets are registered and stacked on the processing tray to form a sheet bundle, the sheet bundle is wire-stitched by the stapler. The wire-stitched sheet bundle is discharged to the stack tray by the sheet bundle discharge roller pair.
Meanwhile, subsequent sheets cannot be conveyed to the processing tray until such a sheet bundle stitching process is executed, the sheets are discharged to the stack tray, and the processing tray is evacuated. Due to this, the sheets conveyed from the image forming apparatus main body during this period are temporarily held on standby in front of the processing tray. This standby process, which is performed by the buffer roller on the buffer path, will be referred to as “buffering” hereinafter. When the processing tray is evacuated, a sheet conveyed next from the image forming apparatus main body is superimposed on the buffered sheets in the buffer path and the resultant sheets are conveyed toward the processing tray.
The finisher that treats sheets having a plurality of sheet sizes has, however, the following disadvantages. Since it is necessary to provide a plurality of buffer paths connecting to the respective sheet sizes, a path configuration and a conveyance control are complicated. This not only makes the apparatus large in size but also deteriorates sheet process reliability.